What is the formula for unit cell volume in terms of the edge length a?

• A. a^3
• B. a^2
• C. 3a
• D. 4a^3

Answer: (A)

The volume of a cube is the product of its three equal edge lengths, so with a cubic unit cell where each edge is a, the volume is a × a × a = a^3. The other options don’t match the geometry: a^2 is the area of a face, 3a has only linear units, and 4a^3 isn’t tied to the cube’s volume. So the unit cell volume is a^3.